This invention relates generally to packet networks and more particularly to a packet network that supports packet header suppression and multiple microflows on the same Service Identification field.
A voice or other type of data stream is transmitted over a packet network by first formatting the data stream into multiple discrete packets. For example, in a Voice over Internet Protocol (VoIP) application, a digitized audio stream is quantized into packets that are placed onto a packet network and routed to a packet telephony receiver. The receiver converts the packets back into a continuous digital audio stream that resembles the input audio stream. A codec (a compression/decompression algorithm) is used to reduce the communication bandwidth required for transmitting the audio packets over the network.
A large amount of network bandwidth is used for overhead when a data steam is converted and transmitted as packets. Voice packets have a certain length according to recording time. Typical recording times are usually 10 or 20 milliseconds. Sending packets with longer recording times increase bandwidth efficiency by reducing the percentage of the packet used for overhead and increase the percentage of the packet used for voice payload. The disadvantage of transmitting packets with more voice payload is that the packets have more latency. Thus, for better performance, smaller voice packets (10 ms) are transmitted that each have a higher percentage of packet overhead. The large amount of network bandwidth used for packet overhead reduces the maximum number of connections that can be established on the network.
Cable modem networks are used to carry VoIP packets and other data between a cable modem termination system and multiple cable modems. The cable modems are identified using a Service Identification (SID) field. The cable modems may carry a diverse amount of traffic, both originating from internal ports and from external ports. Each unique combination of source and destination addresses and ports is referred to as a microflow. The number of SIDs assigned to the cable modem may be limited, either due to hardware limitations or network provisioning limitations. As a result, the number of microflows can exceed the number of available SIDs.
Accordingly, a need remains for a system that more efficiently uses bandwidth in a packet network and can also assign multiple microflows to the same Service Identification field.
Header suppression is used to transport packets more efficiently in a packet network. Header suppression allows more voice calls to be established on a particular physical media without the need for explicit compression. This increases call density with relatively low software overhead. Header suppression is implemented on a per link bases within a network and is a layer 2 service offered for transporting layer 3 and layer 4 protocols. Header suppression is applied to any point-to-point or multipoint-to-point network and is particularly useful in transmitting Voice Over IP (VoIP) packets in a cable network.
A first packet processing node transmits packets having multiple packet headers and a packet payload. The first packet processing node while in a header suppression mode suppresses transmission of one or more of the packet headers. A second packet processing node receives the packets from the first packet processing node over a network medium. The second packet processing node includes memory that contains the packet headers suppressed by the first packet processing node and appends the stored headers to the suppressed header packets before sending the packets to a destination endpoint.
In one example, one of the first and second packet processing nodes comprises a cable modem and the other packet processing node comprises a cable modem termination system (headend). A protocol transmits a header suppression notice between the cable modem and the cable modem termination system. Information is then transmitted identifying the headers to be suppressed. The suppressed header information is stored and then appended to suppressed packets. The appended packets are then routed to another endpoint either on the same cable modem network or on a packet-switched network.
While described in a cable modem network environment, header suppression is applicable between any two processing devices that would have the ability to suppress all or portions of one or more packet headers. For example, header suppression can be used between routers or switches. Header suppression can also be used between non-network processing nodes, such as between a backplane and a disc drive.
Cable modems (CMs) include one or more Service Identification (SID) fields for establishing communication channels (microflows) with a Cable Modem Termination System (CMTS) through a cable medium. In another aspect of the invention, a cable modem protocol is used between the CMTS and the CM to dynamically establish and modify multiple microflows between the CMTS and CM on the same cable modem SID.
The cable modem protocol can be initiated by either the CM or the CMTS. A request signal requests modification to the number of phone calls established on one of the SIDs. A response signal is used to indicate acceptance or non-acceptance of the modification request. An acknowledge signal then verifies SID modification and verifies that network bandwidth allocation has been adjusted according to the modification request.
The foregoing and other objects, features and advantages of the invention will become more readily apparent from the following detailed description of a preferred embodiment of the invention which proceeds with reference to the accompanying drawings.